(1) Technical Field
The subject invention is directed toward a lubrication circuit for a fluid pumping assembly and more specifically to a fluid pumping assembly having a lubrication circuit communicating between a crank case operating at a first pressure and a discharge chamber operating at a second elevated pressure through a control valve.
(2) Description Of The Prior Art
The lubrication of the mechanical working parts housed within a fluid pumping assembly has always been a concern for design engineers. Excessive wear and heat generated by the working parts of a pump can quickly erode optimum working parameters such as volumetric efficiency and can ultimately lead to seizure or other types of failure in the pump.
Proper lubrication is especially important in fluid pumping assemblies such as compressors used to recirculate a refrigerant in an automotive air conditioning application. In compressors of this type, it is important to keep working parts lubricated while limiting the amount of oil which is mixed with the refrigerant so as to prevent excessive oil in the refrigeration circuit. An increased amount of oil in the refrigeration circuit causes a deterioration in the performance of the heat exchanger of the air conditioning system, leading to an inferior refrigerating capacity of the system. Further, the increased amount of oil in the refrigeration circuit causes a shortage of oil within the compressor and consequently insufficient oil to the working parts resulting in seizure or excessive wear as indicated above.
In order to avoid these problems, prior art compressors often include complex lubrication circuits including multiple passages bored through the structure of the housing, valve plate, drive shaft and other elements of the compressor. Examples of compressors having such complex lubrication circuits can be found at U.S. Pat. No. 4,621,983 issued to Thomas et al on Nov. 11, 1986; U.S. Pat. No. 4,432,702 issued to Honzawa on Feb. 21, 1984; U.S. Pat. No. 4,392,788 issued to Nakamura et al on Jul. 12, 1983; U.S. Pat. No. 4,283,997 issued to Takahashi et al on Aug. 18, 1981; U.S. Pat. No. 4,290,345 issued to Hiraga et al on Sep. 22, 1981; U.S. Pat. No. 3,587,406 issued to Gannaway et al on Jun. 28, 1971; and Japanese Patent No. 63-280876 issued to Kobayashi.
Unfortunately, multiple lubrication passages increase the cost of the compressor while not necessarily improving the lubrication of the assembly. Furthermore, special problems can arise when the compressor is tilted or mounted in such a way that the oil collects in one portion of an oil sump or reservoir which is remote from an oil return passage. In these cases and despite an otherwise well designed lubrication circuit, little or no oil is returned to the working elements of the compressor.